tracing: Add synth_event_delete()

create_or_delete_synth_event() contains code to delete a synthetic
event, which would be useful on its own - specifically, it would be
useful to allow event-creating modules to call it separately.

Separate out the delete code from that function and create an exported
function named synth_event_delete().

Link: http://lkml.kernel.org/r/050db3b06df7f0a4b8a2922da602d1d879c7c1c2.1580323897.git.zanussi@kernel.orgAcked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Tom Zanussi <zanussi@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

include/linux/trace_events.h

@@ -354,6 +354,8 @@ extern struct trace_event_file *trace_get_event_file(const char *instance,
 						     const char *event);
 extern void trace_put_event_file(struct trace_event_file *file);
 
+extern int synth_event_delete(const char *name);
+
 /*
  * Event file flags:
  *  ENABLED	  - The event is enabled

kernel/trace/trace_events_hist.c

@@ -1360,29 +1360,54 @@ static int __create_synth_event(int argc, const char *name, const char **argv)
 	goto out;
 }
 
-static int create_or_delete_synth_event(int argc, char **argv)
+static int destroy_synth_event(struct synth_event *se)
 {
-	const char *name = argv[0];
-	struct synth_event *event = NULL;
 	int ret;
 
-	/* trace_run_command() ensures argc != 0 */
-	if (name[0] == '!') {
-		mutex_lock(&event_mutex);
-		event = find_synth_event(name + 1);
-		if (event) {
-			if (event->ref)
+	if (se->ref)
 		ret = -EBUSY;
 	else {
-				ret = unregister_synth_event(event);
+		ret = unregister_synth_event(se);
 		if (!ret) {
-					dyn_event_remove(&event->devent);
-					free_synth_event(event);
+			dyn_event_remove(&se->devent);
+			free_synth_event(se);
 		}
 	}
-		} else
-			ret = -ENOENT;
+
+	return ret;
+}
+
+/**
+ * synth_event_delete - Delete a synthetic event
+ * @event_name: The name of the new sythetic event
+ *
+ * Delete a synthetic event that was created with synth_event_create().
+ *
+ * Return: 0 if successful, error otherwise.
+ */
+int synth_event_delete(const char *event_name)
+{
+	struct synth_event *se = NULL;
+	int ret = -ENOENT;
+
+	mutex_lock(&event_mutex);
+	se = find_synth_event(event_name);
+	if (se)
+		ret = destroy_synth_event(se);
 	mutex_unlock(&event_mutex);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(synth_event_delete);
+
+static int create_or_delete_synth_event(int argc, char **argv)
+{
+	const char *name = argv[0];
+	int ret;
+
+	/* trace_run_command() ensures argc != 0 */
+	if (name[0] == '!') {
+		ret = synth_event_delete(name + 1);
 		return ret;
 	}